Conforce® Constant Force Springs

Vulcan Spring is a leading designer and manufacturer of constant force springs, also called constant tension springs. Conforce is Vulcan Spring’s brand name for its constant force spring, a brand that is well known and highly respected for quality throughout the world. Conforce constant force springs:

  • Offer high force output with very small space requirements
  • Provide long linear reach with minimal force buildup
  • Store power indefinitely when extended

Custom Constant Force Springs

Vulcan Spring specializes in making custom constant force springs to customer specification. With Vulcan Spring’s design, engineering and manufacturing prowess, custom springs can be produced in almost the same time as stock springs. “Custom” is normal for Vulcan Spring and this has been proven to customers over and over again.

How to Work with Vulcan Spring for Custom Constant Force Springs

Vulcan Spring works with our clients at various stages of their product development process with DFM (design for manufacturing) principles. We are design experts with over 40 years' experience in designing and delivering cost effective products in volume. In addition, Vulcan offers a broad range of fully engineered springs from our extensive portfolio of products.

The design and engineering process includes:

  • Initial Design Review
  • Prototyping - usually about 10 to 20 prototype springs
  • Testing
  • Production - Short run or long run production

Technical Considerations for Constant Force Springs

Constant force springs are typically specified and engineered with the following in mind:

  • Diagram demonstrates calculation of space requirements for  constant force springs from Vulcan SpringMaterials - Type 301 stainless steel typically produces the best part at the lowest cost. High-carbon steel, Inconel and other materials are suggested when required.
  • Life in total estimated number of cycles - the life of the constant force spring is very predictable. A life cycle is an extension and retraction of either the whole spring or any portion of it. A low estimate of the life will lead to early failure. A high estimate (the more common error) makes the spring larger and more expensive than is necessary.
Conforce® Design Guide H: Spring Life  = 4,000 cycles Metric
Conforce® Design Guide J: Spring Life = 8,000 cycles Metric
Conforce® Design Guide K: Spring Life = 12,000 cycles Metric
Conforce® Design Guide L: Spring Life = 25,000 cycles Metric
Conforce® Design Guide M: Spring Life = 50,000 cycles Metric
Conforce® Design Guide N: Spring Life = 100,000 cycles Metric
  • Force requirements - the force of the spring should be equal to the requirement of the application. The normal tolerance for a constant force spring is +/-10%
  • Available space - For any force value there are several material thickness and width combinations that can be used. The natural coil diameter depends upon the thickness, life, and force required. A constant force spring does not extend tangent of the coiled body of the spring. For proper operation, constant force springs require .8 x I.D. (see drawing). “A” = Minimum extension needed to achieve rated force = O.D
    • Width
    • Outside diameter
    • Length - allow at least 1 and 1/2 turns to remain when the constant force spring is fully extended.
  • Environment - corrosive atmospheres and/or extreme temperatures will affect the life of the constant force spring performance and influence material selection.
  • End detail - Vulcan Spring has many standard dies to create the end detail; the image shows some that are available. Special end designs can be made for a nominal charge.

       View End Details  


  • Mounting Methods - Vulcan Spring offers a variety of single and multiple mounting recommendations; see image




Mounting Methods for Constant Force Springs

This configuration does not add stability



Offers sum of forces in a limited space


Spool Mounting
A Common Method

Spool Mounting


Cavity Mounting
Low cost, but friction is a limiting factor
Cavity Mounting
Back to Back
Most stable mounting
Back to Back Constant Force Mounting


1. Idler pulleys should not be used because life is reduced by as much as 2/3 at each pulley.

2. Backbending destroys a constant force spring.

Not Recommended

Applications / Uses for Constant Force Springs

Conforce® constant force springs are ideal for a wide variety of uses where constant force / tension springs are needed, including applications requiring smooth returning and retrieving, counterbalancing applications, and tensioning and loading applications. Industries that use constant force springs include:

In some applications, it is desirable for the spring to change force. A spring that produces less force while being extended has a negative gradient. A spring that produces more force when extended has a positive gradient. Vulcan Spring offers both positive gradient constant force springs and negative gradient constant force springs.

Stock Constant Force Springs

Vulcan Spring offers two product lines of stock / standard-sized constant force springs:

  • Series H: spring life of 4,000 cycles, thickness range .003" to .031", width range .187" to 2.00", length from 12" to 60"
  • Series L: spring life of 25,000 cycles, thickness range .004” to .031”, width range .250" to 2.00", length from 18" to 70"

Vulcan Spring’s Manufacturing Process for Constant Force Springs

Vulcan Spring utilizes highly customized production equipment, lean manufacturing techniques and principles, and ISO 9001:2015 certified procedures to provide our customers with a streamlined and efficient manufacturing process.

Benefits of working with Vulcan Spring include reduced lead times, high quality control and highly competitive costs.

Contact Vulcan Spring for Custom Constant Force Springs or Order Stock Custom Constant Force Springs Online

For further assistance with custom constant force springs, complete the request form. We also offer a variety of stock springs online. Order stock Conforce® Constant Force Springs online.